1. Field of the Invention
The present invention relates to an equipment for treating sewage water such as industrial effluent, home life sewage water, etc., and more particularly to a sewage water treatment equipment with activated sludge process beds in which sewage water and air are brought into contact with a carrier (i.e., cultivation bed) on which micro-organisms (i.e., activated sludge) are implanted and cultivated, the activated sludge is bred, and water pollution materials such as BOD, COD are oxidatively decomposed by the activated sludge process beds.
2. Description of Prior Art
Hitherto, an activated sludge process, several modification thereof and tricling filter are conventionally used as one of sewage treatment methods in which such water pollution materials as BOD, COD contained in the sewage water discharged from factories, hotels, homes, etc. are decomposed by micro-organisms. These conventional treatment methods, however, have several disadvantages such as difficulty in daily operation control, necessity of large space for installing the equipment, increase in cost due to a large amount of sludge to be treated and so on.
In addition, a catalytic oxidation method is recently used, wherein micro-organisms are implanted, cultivated and bred on a surface of a catalytic element of a certain design, and the catalytic element is arranged in an aerator to decompose BOD, etc. contained in the sewage water. In such catalytic oxidation method using a catalytic element, however, there exists the same problem as the foregoing conventional methods in the aspect of difficulty in daily operation control, and moreover micro-organisms may sometimes excessively increase to the extent of clogging up the treatment equipment and paralyzing the decomposition of BOD, etc.
In another catalytic oxidation method, in which a corrugated plate of a hard synthetic resin is used as a catalytic element, there exists such problems that it takes long for aerobic bacteria to be implanted and cultivated, that a film formed by bacteria is easy to be peeled due to water flow at the time of aeration or by some physical shock, and that some pieces of the peeled film come to float as scum while the other being precipitated into the bottom of a treatment tank as sludge declining sewage treatment performance thereby.
In a further method for sewage treatment in which a sponge piece is used as a catalytic element floating in an aeration tank, there is a problem that the sponge piece tends to move to one corner of the tank due to water flow at the time of aeration or by wind, eventually inhibiting uniform treatment.
In view of the foregoing problems pertaining to the known methods, the applicant has proposed an activated sludge process bed as disclosed in Japanese laid open Patent Publication (unexamined) No. 59-145096. According to this device, a mesh-like or grid-like outer peripheral surface of a cylindrical core is wrapped with a porous member at a specified thickness to form an activated sludge process bed, and a plurality of such activated sludge process beds are vertically disposed in an aeration tank for sewage treatment. By such arrangement, the device certainly exhibits the following advantages. That is, the activated sludge process beds are not moved by bubbles blown out of an aeration pipe, micro-organism can be implanted and cultivated in short period, and the film of micro-organism is not peeled at all. Furthermore, aerobic bacteria and anaerobic bacteria decompose BOD, COD, etc. further breeding themselves, while other giant micro-organisms are spontaneously bred or come to live at the center portion of the porous member and eat away these aerobic and anaerobic bacteria and autolize them. As a result, it is possible to prevent excessive increase of the aerobic bacteria so as not to produce further sludges. When a plurality of tanks are installed in a row and dissolved oxygen concentration (hereinafter referred to as "DO value") by the aeration is changed tank by tank as well as depending on whether inner periphery or outer periphery of the cylindrical activated sludge process bed, it is expected to perform the sewage treatment efficiently at a high BOD/COD elimination rate by means of respective beds, each having adequate breeding layers formed of aerobic and anaerobic bacteria while balancing nutritively the air, nitrogen and phosphorus they need according to the progress of the treatment.
The sewage treatment method disclosed in the above Publication No. 59-145096 indeed has various advantages as described above, but at the same time following disadvantages are to be pointed out, that is, as a matter of fact, from the viewpoint of operation control, it is quite difficult to control aerobic and anaerobic bacteria accurately so as to keep a correct and desired DO value tank by tank as well as inside and outside of each tank by merely changing the amount of air supplied from the aeration pipe since such other factor as water flow gives influence to the control. Besides, daily operation control in the treatment will require much labor. Accordingly, since the accurate control of DO value is difficult, it will be further difficult to eliminate BOD and COD at high efficiency. In particular, when BOD and/or COD is at lower level, the treatment will be difficult all the more.